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When European settlers had settled on lake Ontario, they began developing several agricultural programs. Those agricultural developments included deforestation. This thus caused plenty of ecosystems and habitats to be lost. The water quality was decaying during this time period. which led to the decline of fishing and several native fishes. During the late 1960s, people began to take action, and wanted to restore the lake. One of the ways they attempted to fix the lake was by reducing the phosphorus levels, New York banned the use of high phosphorus detergents.

chlorophyll concentration

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PHOSPHORUS CONCENTRATION
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This is a chart of nitrogen and phosphorus loading in Lake Ontario


Sources
Industrial
Domestic
Agricultural
Natural
Total
T-N 1967
N.A.
N.A.
N.A.
N.A.
176,000
T-P 1967
N.A.
N.A.
N.A.
N.A.
27,300
1976
102
2,815
3,581
488
11,755*
* Including 4,769 t from upstream lakes.





sources.
http://www.ilec.or.jp/database/nam/nam-07.html
http://www.seagrant.sunysb.edu/glsportfish/pdfs/LOnt-EcoIndicators-Fall08.pdf